In a video I shared two months ago included a wide range of academic studies showing that government-imposed trade barriers undermine economic prosperity.

Not that those results were a surprise. Theory teaches us that government intervention is a recipe for economic harm. And we certainly havepainful historyshowing the adverse consequences of protectionism.

When I debate the issue, I like to cite real-world examples, such as the fact that the nations with the lowest trade barriers tend to be very prosperous while protectionist nations are economic laggards.

No wonder there’s such a strong consensus among economists.

Today, we’re going to add to pro-trade consensus.

A new study from the International Monetary Fund investigates the macroeconomic impact of trade taxes. Here’s the basic outline of the methodology.

Some economies have recently begun to use commercial policy, seemingly for macroeconomic objectives. So it seems an appropriate time to study what, if any, the macroeconomic consequences of tariffs have actually been in practice. Most of the predisposition of the economics profession against protectionism is based on evidence that is either a) theoretical, b) micro, or c) aggregate and dated. Accordingly, in this paper, we study empirically the macroeconomic effects of tariffs using recent aggregate data. …Our panel of annual data is long if unbalanced, covering 1963 through 2014; more recent data is of greater relevance, but older data contains more protectionism. Since little protectionism remains in rich countries, we use a broad span of 151 countries, including 34 advanced and 117 developing countries.

And here are the results.

Our results suggest that tariff increases have adverse domestic macroeconomic and distributional consequences. We find empirically that tariff increases lead to declines of output and productivity in the medium term, as well as increases in unemployment and inequality. … a one standard deviation (or 3.6 percentage point) tariff increase leads to a decrease in output of about .4% five years later. We consider this effect to be plausibly sized and economically significant… Why does output fall after a tariff increase? …a key channel is the statistically and economically significant decrease in labor productivity, which cumulates to about .9% after five years. …Protectionism also leads to a small (statistically marginal) increase in unemployment…we find that tariff increases lead to more inequality, as measured by the Gini index; the effect becomes statistically significant two years after the tariff change. To summarize: the aversion of the economics profession to the deadweight losses caused by protectionism seems warranted; higher tariffs seem to have lower output and productivity, while raising unemployment and inequality. … there are asymmetric effects of protectionism; tariff increases hurt the economy more than liberalizations help.

The simple way to think about this data is that protectionism forces an economy to operate with sand in the gears. Another analogy is that protectionism is like having to deal with permanent and needless road detours. You can still get where you want to go, but at greater cost.

The bottom line is that things simply don’t function smoothly once government intervenes.

Lower growth, reduced productivity, and higher unemployment are obvious and inevitable consequences, as shown in the IMF study.